Abstract
J.Phys.A30:L507-L512,1997 The antiferromagnetic Heisenberg spin chain with N spins has a sector with
N=odd, in which the number of excitations is odd. In particular, there is a
state with a single one-particle excitation. We exploit this fact to give a
simplified derivation of the boundary S matrix for the open antiferromagnetic
spin-1/2 Heisenberg spin chain with diagonal boundary magnetic fields.
